The present invention relates to face shields and especially to motorcycle face shields for attaching to protective helmets and the like, and especially to such a face shield adapted to fit a wide variety of helmets.
In the past, a variety of helmets have been designed for use by motorcycle riders, race car drivers, and the like, to protect the head of a user against damage in the event of an accident. The helmets typically provide a male portion of a snap fastener for attaching thereto, so that a face shield may be attached to the helmet. The face shield protects the user of a motorcycle from the wind, rain, and the like, when riding the motorcycle, and may be snapped off when not needed or desired. It may be easily replaced in the event that the face shield is damaged, inasmuch as a number of manufacturers make helmets, which manufacturers may typically make a matching face shield in which the snap fastener portions are positioned to co-operate with the snap fastener portions on the manufacturers' shield. This has presented somewhat of a problem to provide a shield that will fit all or most helmets on the market. To overcome this problem, a number of solutions have been proposed. One common technique now used for making face shields adaptable to a larger number of helmets has been to mold the face shield with T-shaped slots located over the portion to engage the ear snap fastener of the helmet and also with a vertical slot for the center snap fasteners and a horizontal slot for the two outboard snap fasteners. Female snap fastening portions are then connected with studs through these slots loosely so that the fasteners can slide around in the slots to adjust the positions of the snap fasteners to fit these particular helmets. This has worked satisfactory, but metal snap fasteners which use female sockets with brass or bronze rings mounted therein are expensive to purchase and to attach to the face shield inasmuch as they require snap machines as well as employees to operate the snap machines to place the snap fasteners in place. This results in a number of rejects associated with the snap fastener machinery. In addition, the metal snap fasteners' being loosely fitted with ring snaps therein tend to rattle when wind currents or stresses are put upon the attached face shield. To overcome these problems, one manufacturer has suggested providing a shield with a series of slots in a plastic face shield which will simply snap on the male fasteners of the helmet directly through the slots to hold the face shield in the slots. This however, has proved inadequate because the snap fasteners fit the slots in the same place for each brand helmet and while satisfactory the first few times the shield is snapped upon the helmet, the shield rapidly loosens as the plastic is stretched and even hobbed by the snapping of the male snap fastener through the thin edge of plastic of the slot. One of the difficulties in matching the shield to the helmet has been the use of a center snap along with outboard snaps and ear snaps which require fairly precise lining up of all the snap fasteners. The present invention, on the other hand, eliminates the outboard snap fasteners on the face shield, and has fixed positions for all of the remaining snap fastener portions. Thus, the center female snap fastener portion connects directly to the male center snap fastener portion of the helmet, and without outboard snap fasteners to align that portion of the helmet, the shield can be pulled back into position to engage one of a plurality of female ear snap fasteners. This allows the manufacturer to utilize a face shield of one molded piece, to substantially reduce the cost of making the face shield which does not rattle. The female plastic fasteners thus provide a strong holding action with the metal male fastener portions on the helmet. In addition, male snap fastener portions can be molded directly into the shield for engaging a visor that can be added to the front of the helmet and shield to shade the eyes of a user.
Frequently shields are subjected to high wind speeds while used during racing or normal riding and it becomes advantageous to use the very tightest action snaps so as to prevent the shield from unsnapping and thereby disorienting the wearer which may cause an accident. Since all metal female ring snaps or sockets have a ring which is not unified, they cannot be made as tight as would be possible, since to do so would mean the broken ring would have to be made so small it would be too small to stretch over the male stud portion when attempting to snap it on, and would thereby not snap on at all. It would also stretch the metal beyond its tensile limits resulting in permanent deflection. It is desirable to have a snap ring having a diameter that will work on one or several manufacturers' studs in the same general size class. A hard action socket would be totally unsatisfactory on the smallest of studs to be found (about 0.382 inches-head diameter) and very difficult to use because it would be too hard an action on the largest of studs found (about 0.398 inches-head diameter). An important factor is that less expensive plastics of a transparent optical grade typically have a reasonable freedom from shattering, however, do not work well if manufactured as a socket and stud assembly and affixed to the shield slots such as metal snaps are used. This is because the sockets stretch and permanently deform more and more as they are continually snapped.
In the present snap, the socket's base is a part of the shield thereby preventing stretching and making it possible for a tighter action than metal ring snaps provide. Even a socket made a part of the shield must be made 0.004 to 0.006 inches smaller in diameter than the smallest stud widely marketed, and a 30.degree.-45.degree. entry ramp is desirable in order to make possible the pressure required to snap the socket onto the stud by an average person.
If a polymer such as polycarbonate is used, the interior of the socket must be made large enough that once the socket is snapped onto the stud it is not under continual pressure from the stud diameter pushing against it. Otherwise, it will fail when its stress limits are exceeded (about 500 to 1,000 hours of being snapped onto a helmet). A variety of polymers can be used with the present invention making it possible to manufacture inserts of sockets and seal, or to weld or snap the unit into the shield proper.